An apparatus of this kind is known from U.S. Pat. No. 6,925,993 B1. The centrifugal rotor of the apparatus is driven by pressurized lubricating oil from the combustion engine, wherein the nozzle is arranged to direct the jet of pressurized oil onto the turbine wheel for rotation of the centrifugal rotor. A section through the adapter element is shown (see FIGS. 2 and 3 of U.S. Pat. No. 6,925,993) with the nozzle being situated in a drive oil passage of the adapter element. The nozzle is manufactured by machining a piece of brass material into the shown shape having a trumpet-shaped nozzle passage which converges in the flow direction towards the nozzle opening, after which the machined nozzle is inserted into the drive oil passage of the adapter element.
There is a general desire to improve the separating efficiency of the apparatus, and one way of achieving this is to increase the rotational speed of the centrifugal rotor. This may for instance be done by increasing the size of the nozzle opening to discharge a greater amount of pressurized liquid against the turbine. However, increasing the flow rate in this way will also increase the power take off from the combustion engine used for driving the centrifugal rotor. A road vehicle is equipped with various auxiliary equipment designed to be driven by the combustion engine, and it would therefore be beneficial to limit the power take off by the auxiliary equipment (e.g. for good fuel economy). To increase the efficiency of the drive for the centrifugal rotor in order to achieve as high centrifugal rotor speeds as possible with limited power consumption is thereby desirable. A further important aspect in designing the apparatus is that of providing a simple solution (promoting cost-efficient manufacturing and assembly of the apparatus) with high performance. The adapter element for supplying pressurized liquid to drive the centrifugal rotor is one way of achieving this, yet to further improve this aspect is still very much desirable.